This invention relates to an improved method and apparatus for joining together the ends of a metallic band by resistance inert gas welding.
In the binding or strapping of bales and other bundles of material, wire has long been used and for many years the normal method of joining the opposite ends of such wires together has been a twisted knot. This method has been acceptable for the most part but now under present conditions the conventional twisted wire joint is proving to be unsatisfactory.
The industry now requires a higher joint efficiency because it has become the practice to compress more bulk into smaller packages, resulting in higher stresses on the joints in the wires applied to retain the finished packages or bundles. Also, some of the products now being considered for wire binding exert continuous stress on the wire long after the packages or bundles have been released from the presses used to form them. A twisted wire joint, commonly referred to as a knot, has a tendency to untwist after being exposed to continuing stress.
For example, a sample wire may support a load of 3000 pounds. A twisted joint in the same wire may support a load of only 2700 pounds for a brief time. A twisted joint in the same wire under continuous stress will normally untwist and lose the ability to support a continuous load of only 1800 pounds for 24 hours.
Normally a high density package or bundle is retained with several wires around it to withstand the forces applied by the internal expansion of the package. If any of these wires fail to support their share of the load the remaining wires are subjected to an increased stress beyond their capacity and soon all the joints have failed.
Welded wire joints have heretofore been proposed for such purposes but have not proved to be successful, mostly because of the chemical properties of high tensile steels having a high carbon content along with other alloys that resist normal welding techniques. Oxidation of the metal during welding is a major cause of joint failure owing to improper or inconsistent annealing after welding. The most common failures occur in the metal immediately adjacent to the weld or in the weld joint itself.